Process for the production of solid urea-nitric phosphate fertilizer products

ABSTRACT

The present invention relates to the reaction of phosphate rock with nitric acid and urea to produce nitrogen-phosphorus containing slurries, which slurries may be granulated and dried to produce solid N-P fertilizer products with agronomically advantageous low pHs (1.1-4.0). Products with optimum physical and chemical properties were discovered by investigating the characteristics of each individual material as a function of the nitric acid acidulation ratio (mole ratio HNO 3  :CaO) and the mole ratio urea:CaO present in each product. Acidulation ratios ranged from 1.2 to 2.1 while ratios urea:CaO ranged from 1.6 to 4.0. Selected products with optimum physicochemical properties are tabulated below: 
     
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     Acidulation                                                               
Ratio      Ratio                    Melting                               
HNO 3  :CaO, M/M                                                       
           Urea:CaO, M/M Grade      Pt, °C.                        
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1.2        2.2           23.8--11.7--0                                    
                                    137-139                               
1.4        2.4           25.0--11.0--0                                    
                                    136                                   
1.6        2.8           25.9--9.9--0                                     
                                    133-137                               
1.8        3.0           26.4--9.2--0                                     
                                    134-135                               
2.0        3.3           27.2--8.7--0                                     
                                    130                                   
2.1        3.2           36.6--8.8--0                                     
                                    125-130                               
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Acidulation                                                               
           P 2  O 5  Solubility,                                    
                                 Critical Rela-                           
Ratio      %           pH of 1%  tive Humidity                            
HNO 3  :CaO, M/M                                                       
           Water   Citrate solution                                       
                                   at 25° C., %                    
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1.2        69.2    82.1    2.5     59.3                                   
1.4        81.8    90.0    2.4     60.9                                   
1.6        88.9    91.9    2.3     60.1                                   
1.8        96.7    98.9    2.1     59.9                                   
2.1        99.0    100     2.1     60.0                                   
2.1        100     100     2.1     59.5                                   
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     The products have excellent storage characteristics. The improved properties of these products result partially from the formation of a new compound, Ca(H 2  PO 4 )(NO 3 ).CO(NH 2 ) 2 , which was discovered during the course of the investigation that led to the instant invention.



